Large-Z limit in atoms and solids from first principles

Area of Science:

• Computational Materials Science
• Quantum Chemistry
• Solid-State Physics

Background:

• Density functional theory (DFT) is a powerful quantum mechanical modeling method.
• Approximations in DFT, such as orbital-free functionals, aim to reduce computational cost.
• Accurate calculation of material properties like ionization potentials and lattice constants is crucial.

Purpose of the Study:

• To compare the accuracy of different kinetic energy functional approximations in DFT.
• To investigate the performance of orbital-free DFT against Kohn-Sham DFT across a range of atomic numbers (Z).
• To evaluate the impact of nuclear potential treatment (all-electron vs. pseudopotentials) in orbital-free DFT.

Main Methods:

• Performed density functional theory (DFT) calculations.
• Utilized Kohn-Sham (KS) and various orbital-free (OF) kinetic energy functional approximations.
• Employed all-electron (projector augmented wave) and local pseudopotential methods for nuclear potential treatment.

Main Results:

• All-electron orbital-free DFT reproduces the general trends of KS DFT for ionization potentials and lattice constants at moderate Z.
• Significant deviations between all-electron orbital-free DFT and KS DFT are observed for high Z values.
• Local pseudopotentials in orbital-free DFT provide a better qualitative agreement with KS DFT by incorporating shell oscillations.

Conclusions:

• Orbital-free DFT offers a computationally efficient alternative to KS DFT for certain properties and atomic number ranges.
• The choice of nuclear potential treatment significantly impacts the accuracy of orbital-free DFT, especially for heavy elements.
• Both all-electron orbital-free DFT and KS DFT predict finite nonrelativistic lattice constants in the large-Z limit.